zend，如何使用数字和文本添加multiOption？

i have a zend drop down style code:

$this->addElement('select', 'waistmin', array(
            'label' => 'Pants:',
            'multiOptions' => array_combine(range(21, 48), range(21, 48)),
            'value' => 21
    ));

this will do :

<select id="waistmin" name="waistmin">
<option selected="selected" label="21" value="21">21</option>
<option label="22" value="22">22</option>
.......
<option label="47" value="47">47</option>
<option label="48" value="48">48</option>
</select>

what i want to do is to add an array('', 'Any') option so the code will have the Any option as the first one and selected by default.

and im not sure how to add this option inside the array_combine

any ideas? thanks

'multiOptions' => array_merge(array(''=>'', 'Any'=>'Any'), 
                              array_combine(range(21, 48), range(21, 48))
                             )